In Multiple Personality Disorder (Dissociative Identity Disorder, or DID), the emotions are segregated into personality-like internal constructs ("entities"). The notion of "unique separate multiple whole personalities" is primitive and untrue. DID is a continuum. The inner language breaks down into polyglot chaos. In DID, emotions cannot communicate with each other for fear of provoking overwhelming pain (and its fatal consequences). So, they are being kept apart by various mechanisms (a host or birth personality, a facilitator, a moderator and so on).
All personality disorders involve a modicum of dissociation. But the narcissistic solution is to emotionally disappear altogether. Hence, the tremendous, insatiable need of the narcissist for external approval. He exists only as a reflection. Since he is forbidden to love his true self â he chooses to have no self at all. It is not dissociation â it is a vanishing act.
NPD is a total, "pure" solution: self-extinguishing, self-abolishing, entirely fake. Other personality disorders are diluted variations on the themes of self-hate and perpetuated self-abuse. HPD is NPD with sex and body as the source of the Narcissistic Supply. The Borderline Personality Disorder involves lability, the movement between poles of life wish and death wish and so on.
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 2 DVDs with 12 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)